In this proposal several issues relating to the structural and functional organization of the somesthetic system are to be investigated. These are: (A) The synaptic organization of marginal zone. (B) The source of axo-axonic endings on Primary Afferents (P.A.s) in the dorsal horn and spinal nucleus of the trigeminal; concomitantly with this study, the source of other boutons ending on other neurons in the dorsal horn may also be revealed. (C) A re-evaluation of the paleospinothalamic system with regard to the level in the brain stem at which the relay/s take/s place. (D) An effort to correlate P.A. sensory modality with level and manner of termination in the spinal trigeminal complex.